1. Field of the Invention
The present invention relates in general to pneumatic conveyor systems. In particular, the present invention relates to an improved apparatus for introducing granular, cylindrical or flake material, particularly for human consumption, into the airstream of a pneumatic conveying system.
2. Description of the Related Art
The advantages of pneumatic conveying systems have long been known. For example, pneumatic conveying systems have few moving parts, and thus are reliable and relatively efficient. Additionally, when used with food products intended for human consumption, the closed nature of the pneumatic conveying system assists in preventing contamination of the food product.
However, there are certain food products which have heretofore not been suitable for conveyance by pneumatic systems. In particular, ready-to-eat (RTE) cereals such as Rice Krispies.RTM., Cheerios.RTM., Fruit Loops.RTM. and corn flakes, and RTE cereal components such as cylindrical (or other shaped) marshmallow bits, have experienced unsatisfactory results during pneumatic conveyance. During such attempts it was found that the RTE cereal would bridge in the vessel holding the cereal for introduction to the airstream or plug the pneumatic conduit, impeding air and product flow. The continued provision of the entraining air up stream of the bridge would cause increased pressure in this area of the conduit, with the pressure finally reaching a sufficient level to force the material to unclog the conduit.
This unbridging of the material was rather violent, and was immediately followed by a period of higher than normal conveyance speed due to the higher than normal pressure. Both of these events caused unacceptable amounts of breakage of the material, resulting in fines. Such fines are undesirable because they tend to coat the cereal, reducing its luster, and additionally compact the density of the cereal to make weight-based packages appear to contain an insufficient amount of the product by reducing the volume per unit weight.
The present inventors have determined that a major cause for the bridging of the cereal within the conduit is fluctuations in the amount of material introduced into the pneumatic conveying system. For example, materials are mainly introduced into a pneumatic conveying system by one of two methods. In the first method batches of the material pass from an unpressurized hopper open to the atmosphere, through a baffle chamber or pressure lock, and finally into a second hopper open to the conveying air stream, and thus at an elevated pressure equal to that in the conveying conduit. The pressure lock maintains the pressure within the second vessel, and the conveying airstream is continuous. In the second method the material is placed in a vessel and the vessel is sealed. Thereafter the conveying air is activated to convey all material from the vessel, at which point the air is deactivated, and the vessel opened to receive new material. This procedure is repeated as required.
While such a pressurized vessel is necessary to maintain the required pressure within the conveying conduit, the introduction of the material into the airstream has heretofore been non-uniform.